Microsoft Exchange Server 2016 Cumulative…: Improper Neutralization of Input During Web Page Generation
CVE-2026-69356 is a critical-severity improper neutralization of input during web page generation vulnerability in Microsoft Exchange Server 2016 Cumulative Update 23 from Microsoft, with a CVSS 3.1 base score of 9.3 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. The record lists version 15.01.2507.073 as the first without the flaw, so updating Microsoft Exchange Server 2016 Cumulative Update 23 to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.76% chance of exploitation within 30 days, higher than 56% of scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Microsoft Exchange Server 2016 Cumulative Update 23 to 15.01.2507.073 or a later version.
- Update Microsoft Exchange Server 2019 Cumulative Update 14 to 15.02.1544.046 or a later version.
- Update Microsoft Exchange Server 2019 Cumulative Update 15 to 15.02.1748.051 or a later version.
- Read the advisory on msrc.microsoft.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 23 | 15.01.0.0 up to, but not including, 15.01.2507.073 | 15.01.2507.073 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 14 | 15.02.0.0 up to, but not including, 15.02.1544.046 | 15.02.1544.046 |
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 15 | 15.02.0.0 up to, but not including, 15.02.1748.051 | 15.02.1748.051 |
| Microsoft | Microsoft Exchange Server Subscription Edition RTM | 15.02.0.0 up to, but not including, 15.02.2562.049 | 15.02.2562.049 |
| Microsoft | Exchange Server | 2016; 2019 | Not stated |
| Microsoft | Exchange Server Subscription Edition | before 15.02.2562.049 | 15.02.2562.049 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- Scope
- ChangedThe attack can reach beyond the vulnerable component into other systems.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N. Scored by CNA (microsoft.com).
Official description
Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Neutralization of Input During Web Page Generation
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
How developers prevent this class of flaw
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Examples of libraries and frameworks that make it easier to generate properly encoded output include Microsoft's Anti-XSS library, the OWASP ESAPI Encoding module, and Apache Wicket.
- Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.
- For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
More Improper Neutralization of Input During Web Page Generation vulnerabilities (CWE-79)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Other vulnerabilities in Microsoft Exchange Server 2016 Cumulative Update 23
- 9.3 Critical severity
- 8.8 High severity
- 9.6 Critical severity
- 8.1 High severity
- 6.1 Medium severity
Recent Improper Neutralization of Input During Web Page Generation vulnerabilities
- 9.0 Critical severity
- 8.7 High severity
- 8.5 High severity
- 9.3 Critical severity
- 9.3 Critical severity
- 8.7 High severity
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